Simple Summary
Add a IS_STATIC (0x4A) opcode that pushes 1 if the current context is static (ie. the execution is in a STATICCALL or a descendant thereof, so state-changing operations are not possible), and 0 if it is not.
Abstract
Motivation
The main intended use case is to allow account abstraction (EIP 2938) to be extended so that accounts can allow static calls from the outside (which are harmless to AA's security model) but not state-changing calls.
Specification
Add a IS_STATIC (0x4A) opcode that pushes 1 if the current context is static (ie. the execution is in a STATICCALL or a descendant thereof, so state-changing operations are not possible), and 0 if it is not.
Rationale
Determining staticness is already possibly using the following hacky technique: make a CALL with limited gas, and inside that CALL issue one LOG and exit. If the context is static, the CALL would fail and leave a 0 on the stack; if the context is non-static, the CALL would succeed. However, this technique is fragile against changes to gas costs, and is needlessly wasteful. Hence, the status quo neither allows a reasonably effective way of determining whether or not the context is static, nor provides any kind of invariant that executions that do not fail outright will execute the same way in a static and non-static context. This EIP provides a cleaner way of determining staticness.
Backwards Compatibility
TBD
Security Considerations
TBD
Copyright
Copyright and related rights waived via CC0.
